The present invention relates to a process for optical resolution of racemic lysine sulphanilate. It is known, for example in British patent specifications Nos. 1,191,100 and 1,250,557, that racemic lysine sulphanilate can be resolved optically by subjecting a supersaturated solution of racemic lysine sulphanilate to selective crystallization and by separating the optically active lysine sulphanilate, which has then crystallized out, from the mother liquor. From the L-lysine sulphanilate so obtained, L-lysine, as such or in the form of a customary L-lysine compoud, can be recovered, which is useful as an additive for human and animal food.
The use of sulphanilic acid as an auxiliary acid for optical resolution of racemic lysine has an advantage, in comparison with the use of another optically active auxiliary acid, in that it does not itself become racemized during the various processing steps. A disadvantage to the use of sulphanilic acid for optical resolution of racemic lysine, however, is that the yield of optically active lysine sulphanilate in the selective crystallization is rather small, so that a much larger recirculation is necessary than would be the case with the use of an optically active acid, for instance optically active alpha-phenoxypropionic acid, in which the required diastereoisomer-salt can be separated off with a very satisfactory yield through fractional crystallization.